Systems and methods for multi-state switch networks

ABSTRACT

Systems and methods for multi-state switch networks and multi-state LED networks are provided. Systems and methods for maintaining the brightness of LEDs in multi-state LED networks are also provided. The multi-state networks contain control circuitry that can output a single control signal that is able to drive a pair of diodes in three different states. In a network of 2*N diodes, N wires are sufficient to drive the diodes in 3N different states. The control circuitry may also include a pulse-width modulator that controls the perceived brightness of the LEDs in a multi-state LED network in response to a voltage level of the power source.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 60/878,852, filed Jan. 5, 2007 and U.S. ProvisionalPatent Application No. 60/937,853, filed Jun. 28, 2007, each of whichare hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

This relates to multi-state switch network and more particularly tomulti-state light-emitting diode (LED) network systems and methods. Thisalso relates to systems and methods for maintaining the brightness ofthe LEDs within the multi-state LED network independent of batteryvoltage levels.

Typically, each switch within a switch network requires its own controlsignal. When these control signals are connected between multiplecircuits and circuit boards, each control signal also requires its ownI/O pin ON each circuit board. The same is true for LED circuits, whichtypically require individual control signals and pins to operate eachLED. As the number of control signals and pins increases, the size ofthe circuit also increases.

Accordingly, what is needed are systems and methods for multi-stateswitch networks and multi-state LED networks that require fewer controlinputs and that reduces the space required for control signals and pins.

The brightness of an LED varies based on the supplied voltage.Therefore, in battery-powered LED systems, the brightness of the LED isreduced as the voltage of the battery declines.

Accordingly, what is needed is a multi-state LED network that maintainsthe brightness of the LEDs substantially independently of the suppliedvoltage.

SUMMARY OF THE INVENTION

Systems and methods for multi-state switch networks and multi-state LEDnetworks are provided. Systems and methods for maintaining thebrightness of LEDs in multi-state LED networks are also provided.

A multi-state switch network can control the states of two switchesusing only one control signal. In a multi-state LED network, two LEDscan be controlled using only one control signal. These multi-statenetworks contain control circuitry that is connected to a pair ofserially connected diodes. In a switch network embodiment, the diodescan be connected to switches. In a LED network embodiment, the diodesare LEDs. The control circuitry outputs a single control signal that isable to drive the pair of diodes in three different states. In a networkof N diode pairs, N wires are sufficient to drive the 2*N diodes of theN diode pairs in 3^(N) different states.

The control circuitry may also include a pulse-width modulator thatcontrols the perceived brightness of the LEDs in a multi-state LEDnetwork. Pulse-width modulation can be used to vary the perceivedbrightness of an LED. A pulse-width modulated source connected to theLED can be used to turn the LED ON and OFF at a rate undetectable to thehuman eye. Increasing the amount of time the LED is turned OFF makes theLED appear dimmer while increasing the amount of time the LED is turnedON makes the LED appear brighter. Controlling the pulse-width modulationbased at least in part on the battery voltage levels allows the controlcircuitry to maintain the brightness of the LEDs within the multi-stateLED network substantially independently of supplied voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention, its nature andvarious advantages will become more apparent upon consideration of thefollowing detailed description, taken in conjunction with theaccompanying drawings, in which like reference characters refer to likeparts throughout, and in which:

FIG. 1 shows a schematic diagram of illustrative multi-state switchnetwork 100 in accordance with an embodiment of the present invention.

FIG. 2 shows a schematic diagram of illustrative multi-state switchnetwork 200 implemented in separate circuits in accordance with anembodiment of the present invention.

FIG. 3 shows a schematic diagram of illustrative multi-state switchnetwork 300 having N diode pairs in accordance with an embodiment of thepresent invention.

FIG. 4 shows a timing diagram that illustrates the operation ofmulti-switch network 100 in accordance with an embodiment of the presentinvention.

FIG. 5 shows a schematic diagram of an illustrative multi-state LEDnetwork 500 with a pulse-width modulator in accordance with anembodiment of the present invention.

FIG. 6A shows a continuous signal with a 100% duty cycle that may beused to drive multi-state LED network 500 in accordance with anembodiment of the present invention.

FIG. 6B shows a continuous signal with a 66% duty cycle that may be usedto drive multi-state LED network 500 in accordance with an embodiment ofthe present invention.

FIG. 6C shows a continuous signal with a 50% duty cycle that may be usedto drive multi-state LED network 500 in accordance with an embodiment ofthe present invention.

FIG. 7 is a simplified block diagram of a system that incorporates amulti-state switch network in accordance with an embodiment of thepresent invention.

FIG. 8 is a flowchart of an illustrative process in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Commonly assigned Terlizzi et al. U.S. patent application Ser. No.______, filed ______ (Attorney Docket No. 104677-0014 (P4672US1)),entitled “Symmetrical Connector Utilizing Magnetic Attachment Method” ishereby incorporated by reference in its entirety.

FIG. 1 shows a schematic diagram of illustrative multi-state switchnetwork 100. Multi-state switch network 100 includes diode pair 110 andcontrol circuitry 120. Control circuitry 120 controls the operation ofdiodes 104 and 106 within diode pair 110 using a single control signal103.

In one embodiment, diodes 104 and 106 are light-emitting diodes (LEDs).An LED can be directly driven to turn ON and turn OFF. In anotherembodiment, diodes 104 and 106 are connected to switches and the diodesmay be driven to turn those switches ON and OFF. For example, nodes 112and 114 may be connected to any suitable switches (not shown) including,for example, transistor switches, buffers, or any other logic circuits.For ease of explanation, in both embodiments the diodes will be referredto as being turned ON or OFF to indicate their states regardless ofwhether they are directly turned ON and OFF (e.g., an LED) or used toturn ON and OFF another device (e.g., a diode connected to a switch).

Diode pair 110 includes two diodes 104 and 106 connected in seriesbetween Vcc and ground. Diodes 104 and 106 can be of the same type or ofdifferent types. For example, diodes 104 and 106 can be differentcolored LEDs. Control signal 103, connected to control node 108,controls the state of diode pair 110. When a high voltage level controlsignal is applied to control node 108, diode 106 is turned ON and diode104 is turned OFF. When a low voltage level control signal is applied tocontrol node 108, diode 104 is turned ON and diode 106 is turned OFF.When no voltage is applied to control node 108, both diodes 104 and 106can be turned OFF. When no voltage is applied to control node 108 by thecontrol signal, control signal 103 is said to be in a high-impedance orHIGH-Z state. Thus, the two diodes of diode pair 110 may be operated inthree different states using only a single control signal. These threestates are illustrated in Table 1. The operation of diode pair 110 isillustrated in greater detail below with reference to the timing diagramof FIG. 4.

TABLE 1 Three States of Diode Pair 110 Control 103 Diode 104 Diode 106LOW-V ON OFF HIGH-V OFF ON HIGH-Z OFF OFF

Diode pair 110 also includes resistors 105 and 107. The values ofresistors 105 and 107 may be selected to provide appropriate biasvoltage levels to diodes 104 and 106. When properly biased, the voltageacross each of the diodes may be approximately equal to the thresholdvoltages of the diodes when the diodes are supposed to be turned ON andthe voltage across each of the diodes may be below the threshold voltageof the diodes when the diodes are supposed to be turned OFF. Differenttypes of diodes have different threshold voltage levels, which mayaffect the selection of resistors 105 and 107. Thus, the values ofresistors 105 and 107 may be selected based on the voltage levels of thesystem and the properties of diodes 104 and 106.

Control circuitry 120 can be used to generate control signal 103 that isused to control diode pair 110. Control circuitry 120 can includetri-state buffer 121. Tri-state buffer 121 receives input signal 122 andON/OFF signal 123 and outputs control signal 103. ON/OFF signal 123 canbe used to switch diodes 104 and 106 of diode pair 110 ON and OFF. WhenON/OFF signal 123 is ON, input signal 103 can be used to select whichone of diodes 104 and 106 is turned ON. Additional circuitry thatgenerates signals 122 and 123 can also be included within controlcircuitry 120 or can be received from another circuit.

Diode pair 110 and control circuitry 120 can be connected togetherwithin the same circuits as shown in FIG. 1 or may be located inseparate circuits as shown in FIG. 2. FIG. 2 shows control circuitry 220implemented in a first circuit 200 a and LED pair 210 implemented in asecond circuit 200 b. Circuits 200 a and 200 b are connected using anysuitable wire or connector 230. For example, connector 230 may be usedto connect the first circuit 200 a and the second circuit 200 bimplemented on flexible printed circuit boards.

FIG. 3 shows a network of N diode pairs 310 connected to control circuit320. Diode pairs 310 and control circuit 320 are the same orsubstantially similar to their counterparts in multi-state switchnetwork 100. In this arrangement, the 2*N diodes of the N diode pairs310 can be controlled using only N control signals 303 that are outputfrom control circuit 320. Control circuit 320 can have a drive strengthapproximately N times the drive strength of control circuit 120 (FIG. 1)in order to drive the N control signals 303. As described above withrespect to multi-state switch network 100, each of the N diode pairs 310can be driven to three different states using only one control wire.Thus, it can be seen that the 2*N diodes of the N diode pairs 310 can bedriven to 3^(N) different states using only N wires. Thus, the number ofwires and connectors that are required to control a plurality of LEDs orswitches may be reduced.

FIG. 4 shows a timing diagram 400 which illustrates the operation ofmulti-state switch network 100. At time 400, ON/OFF signal 123 is at alow voltage level. Thus, tri-state buffer 121 (FIG. 1) is turned OFF,control signal 103 is in a high-impedance state, and both diodes 104 and106 are turned OFF. At time 401, ON/OFF signal 123 is switched to a highvoltage level, turning ON tri-state buffer 121. Input signal 122 is at alow voltage level and therefore control signal 103 is also at a lowvoltage level. In response to the transition of control signal 103 froma high-impedance state to a low voltage level, diode 104 is turned ONand diode 106 remains OFF. At time 402, input signal 122 is driven to ahigh voltage level, which switches control signal 103 to a high voltagelevel. In response to this transition, diode 104 turns OFF and diode 106turns ON. At time 403, input signal 422 is brought to a low voltagelevel, therefore control signal 103 is also brought to a low voltagelevel. In response, diode 104 turns ON and diode 106 turns OFF. Finally,after time 404, ON/OFF signal 122 is cycled between a high voltage leveland a low voltage level, which causes output signal 103 to cycle betweena low voltage level and a high-impedance state. As a result, Diode 104is cycled ON and OFF. LED 106 remains turned OFF for this entire period.

When used in a battery-powered system, the perceived luminous intensityor brightness of an LED may decrease as battery voltage level decreases.However, if the brightness of an LED can be adjusted, the brightness ofthe LED can be increased as the battery voltage decreases in order tokeep the brightness level of the LED substantially constant.

FIG. 5 shows a schematic diagram of an illustrative multi-state LEDnetwork 500 with a pulse-width modulator 550 that is adjustable tocontrol the perceived brightness of the LEDs. Multi-state switch network500 includes diode pair 510 and control circuitry 520, which are thesame or substantially similar to their counterparts in multi-stateswitch network 100. Diode pair 510 contains two LEDs 504 and 506.

Pulse-width modulator 550 can be used to control the perceivedbrightness of LEDs 504 and 506. Whenever LEDs 504 or 506 are turned ON,pulse-width modulator 550 causes tri-state buffer to generate a controlsignal 503 that provides diode pair 510 with a series of discrete pulsesinstead of a continuous high or low voltage signal. As a result, LEDs504 and 506 are rapidly pulsed ON and OFF rather then being ONcontinuously. When the pulse rate is sufficiently quick, the human eyeis unable to detect the pulsing and will instead see the LED ascontinuously ON.

Duty cycle is a measure of the ratio of the duration of a particularphenomenon in a given period to the duration of the period. In thisinstance, the phenomenon is the duration that the LED is turned ON.Thus, when the LED is continuously turned ON it has a duty cycle of 1 or100%. Varying the duty cycle of ON/OFF signal 523, which varies the dutycycle of control signal 503, controls the duty cycle of the LED andtherefore the perceived brightness of the LED. Reducing the duty cycleof the LED reduces the perceived brightness of the LED, while increasingthe duty cycle of the LED increases the perceived brightness of the LED.

FIG. 6A shows a continuous high voltage signal, i.e., a high voltagesignal with a 100% duty cycle. FIG. 6B shows the same high voltagesignal of FIG. 6A with a 66% duty cycle and 6C shows the same signalwith a 50% duty cycle. The signal with the highest duty cycle (i.e.,FIG. 6A), when applied to control circuitry 520, may cause LED 506 toappear brighter than when the signals with lower duty cycles are applied(i.e., FIGS. 6B and 6C). The signal of FIG. 6C may cause the lowestperceived brightness of the three signals.

Pulse-width modulator 550 has a modulation control input 551 that can beused to vary the duty cycle of the output of pulse-width modulator 550in order to control the perceived brightness of LEDs 504 and 506. PWMcontrol input 551 can receive a signal from a battery voltage levelmonitor (not shown) that is indicative of the charge of the battery. Thebattery voltage monitor can include, for example, an analog to digitalconverter (ADC), a comparator with adjustable thresholds, or multiplecomparators with set thresholds, or any other suitable circuitry. Whenthe battery fully charged, pulse-width modulator 550 may be set toprovide the LEDs with a decreased perceived brightness level. Then asthe battery voltage level decreases, PWM control input 551 can controlpulse-width modulator 550 to increase the perceived brightness levels ofthe LEDs to compensate for the diminished voltage provided to the LEDs.

For example, a signal with a 50% duty cycle may cause the LEDs toprovide sufficient perceived brightness when the battery at a fullycharged voltage level, but as the battery weakens the duty cycle may beincreased to 75% to increase the perceived brightness of the LEDs. Thus,by increasing the perceived brightness of the LEDs as the batteryvoltage level decreases, the perceived brightness of the LED may bemaintained at a substantially constant level independent of the voltagelevel of the battery.

FIG. 7 shows a simplified block diagram of a system that incorporates amulti-state switch network. System 700 includes processor circuitry 710,power distribution circuitry 720, and switch network circuitry 730.Processor circuitry 710 can include a processor and auxiliary circuitrythat works with the processor. Processor circuitry 710 can coordinateall of the operations in system 700, including, for example, controllingpower distribution circuitry 720 and switch network 730. In someembodiments, processor circuitry 710 may include control circuitry(e.g., control circuitry 120 of FIG. 1) that may provide control signalsto switch network 730. Switch network 730 may include one or more diodeor LED pairs, each controlled by a signal control signal.

Power distribution circuitry 720 can include over-voltage protection andfuse 721, li-poly battery protection 722 and thermistor 723.Over-voltage protection and fuse 721 can protect system 700 in the eventthat an unsafe amount of voltage is applied to one or more inputs. Thefuse in the protection circuitry can be any over-current protectiondevice which disconnects the circuit it is coupled with if anover-current condition is present. Li-Poly battery protection circuitry722, can include circuitry to prevent the malfunction of a li-polybattery which could result in a dangerous overheating situation. Li-polybattery protection circuitry 722 is typically built into battery packsas integrated protection circuitry. In accordance with the presentinvention, this circuitry can be separated from the battery and locatedanywhere within system 700. Thermistor 723 can be located in theproximity of a battery (not shown) so that the resistance of thethermistor is indicative of the battery's temperature. One or moreinputs of processor circuitry 710 can be electrically coupled withthermistor 733 so that the processor can monitor the temperature of thebattery. Processor 710 can be programmed to charge the batterydifferently depending on the temperature of the battery. For example,processor 710 can vary the battery charging current according to thedetected temperature. In order to extend the life of a battery, it isbeneficial to charge the battery only when it is within a certaintemperature range. By regulating the charging in this manner, one canextend the life of a battery beyond what would typically be expected.Power distribution circuitry 720 can also monitor the charge level ofthe battery and provide this information to switch network 730 in orderto adjust the perceived brightness of any LEDs located within switchnetwork 730. This battery charge level information can be provideddirectly from power distribution circuitry 720 to switch network 730 ormay be provided by way of processor circuitry 710.

A detailed description of the design and function of exemplary systemsthat can incorporate circuits similar to switch network 730 can be foundin the U.S. patent application entitled “Symmetrical Connector UtilizingMagnetic Attachment Method,” which is incorporated herein.

FIG. 8 shows a flowchart of process 800 for adjusting the perceivedbrightness of an LED within a multi-state LED network in accordance withthe present invention. At step 810, a diode pair receives a controlsignal that turns ON an LED in a diode pair. For example, in LED network500 of FIG. 5, diode pair 510 may receive a high voltage level controlsignal 503 that turns ON LED 506. At step 820, the voltage level of apower source, such as a battery, can be monitored until there is achange in the voltage level at step 830. If there is a change in thevoltage level, at step 840 the duty cycle of the control signal can beadjusted. For example, with reference to LED network 500 of FIG. 5, ifthe voltage level decreases, PWM control signal 551 can be adjustedwhich may cause pulse-width modulator 550 to increase the duty cycle ofcontrol signal 503. This increase in the duty cycle of control signal503 may increase the perceived brightness of LED 506, which may offsetany decrease in the perceived brightness caused by any reduction in thevoltage level.

Thus it is seen that the systems and method for multi-state switchnetworks are provided. Those skilled in the art will appreciate that theinvention can be practiced by other than the described embodiments,which are presented for purposes of illustration rather than oflimitation, and the invention is limited only by the claims whichfollow.

1. A multi-state switch network comprising: a serially-connected diodepair that receives a single control signal; and wherein the singlecontrol signal is operative to drive the serially-connected diode pairto one of at least three different states.
 2. The multi-state switchnetwork of claim 1, wherein the serially-connected diode pair comprisesa pair of LEDs.
 3. The multi-state switch network of claim 2, furthercomprising a pulse-width modulator that modulates the single controlsignal to control a perceived brightness level of the pair of LEDs. 4.The multi-state switch network of claim 3, wherein the pulse-widthmodulator is operative to adjust a duty cycle of the single controlsignal based on a monitored voltage level.
 5. The multi-state switchnetwork of claim 1, wherein the serially-connected diode pair isoperative to control a pair of switches.
 6. The multi-state switchnetwork of claim 1, wherein the control signal comprises one of a highvoltage level signal, a low voltage level signal, and a high-impedancesignal.
 7. The multi-state switch network of claim 1, wherein thecontrol signal is operative to alternatively: turn ON a first diode ofthe diode pair and turn OFF a second diode of the diode pair; turn OFFthe first diode and turn ON the second diode; and turn OFF the firstdiode and turn OFF the second diode.
 8. The multi-state switch networkof claim 1, wherein the serially-connected diode pair consistsessentially of two diodes and two resistors in serial communication. 9.The multi-state switch network of claim 1, further comprising atri-state buffer that provides the control signal.
 10. A plurality ofserially-connected diode pairs as defined in claim 1, each of theserially-connected diode pairs controlled by a single control signal.11. A multi-state switch network comprising: a first diode and a seconddiode that receive a single control signal, wherein the single controlsignal is operative to alternatively: turn OFF the first diode and turnON the second diode; turn ON the first diode and turn OFF the seconddiode; and turn OFF the first diode and turn OFF the second diode. 12.The multi-state switch network of claim 11, further comprising turningOFF the first diode and turning ON the second diode in response to ahigh voltage level control signal.
 13. The multi-state switch network ofclaim 11, further comprising turning ON the first diode and turning OFFthe second diode in response to a low voltage level control signal. 14.The multi-state switch network of claim 11, further comprising turningOFF the first diode and turning OFF the second diode in response to ahigh-impedance control signal.
 15. A multi-state switch networkcomprising: a power source; a ground source; a first LED electricallycoupled to the power source; a first resistor electrically coupled tothe first LED; a second resistor electrically coupled to the firstresistor; a second LED electrically coupled to the second resistor andthe ground source; and control circuitry electrically coupled to a nodeexisting between the first and second resistors, the control circuitryoperative to selectively turn the first and second LEDs ON and OFF byproviding a control signal to the node.
 16. The multi-state switchnetwork of claim 15, wherein when the control signal is a high voltagelevel control signal, the first LED is turned OFF and the second LED isturned ON.
 17. The multi-state switch network of claim 15, wherein whenthe control signal is a low voltage level control signal, the first LEDis turned ON and the second LED is turned OFF.
 18. The multi-stateswitch network of claim 15, wherein when the control circuitry is turnedOFF, the first LED is turned OFF and the second LED is turned OFF.
 19. Amethod of controlling a multi-state switch network comprising first andsecond diodes, the method comprising: receiving a single control signal;and in response to the single control signal, alternatively: turning ONthe first diode and turning OFF the second diode; turning OFF the firstdiode and turning ON the second diode; and turning OFF the first diodeand turning OFF the second diode.
 20. The method of claim 19, whereinthe first diode and the second diode are LEDs.
 21. The method of claim20, further comprising pulse-width modulating the single control signalto control a perceived brightness level of the LEDs.
 22. The method ofclaim 21, further comprising: monitoring a voltage level of a powersource; and adjusting a duty cycle of the control signal based on themonitored voltage level.
 23. The method of claim 19, further comprising:switching a first switch in response to turning ON the first diode; andswitching a second switch in response to turning ON the second diode.24. A system for controlling a multi-state LED network, the systemcomprising: processor circuitry; power distribution circuitry; a switchnetwork comprising first and second diodes, wherein the switch networkis operative to: receive a single control signal from the processorcircuitry; receive voltage level control signal from the powerdistribution circuitry; drive the first and second diodes to one of atleast three different states in response to the single control signal;and adjust a duty cycle of the single control signal based on thevoltage level control signal.